span builder

src/core/position/span.rs

@@ -1,3 +1,5 @@
+use std::marker::PhantomData;
+
 use crate::prelude::*;
 
 pub struct Span {
@@ -15,13 +17,13 @@ impl Widget for Span {
             let mut axis = child_region.axis_mut(self.dir.axis);
             axis.top_left.set(start);
             let len = painter.size(child).axis(self.dir.axis);
-            start.abs += len.abs;
-            start.rel += len.rel;
             if len.rest > 0.0 {
                 let offset = UiScalar::new(total.rel, total.abs);
                 let rel_end = UiScalar::from_anchor(len.rest / total.rest);
                 start = rel_end.within(start, (UiScalar::rel_max() + start) - offset);
             }
+            start.abs += len.abs;
+            start.rel += len.rel;
             axis.bot_right.set(start);
             if self.dir.sign == Sign::Neg {
                 child_region.flip(self.dir.axis);
@@ -75,3 +77,40 @@ impl Span {
         })
     }
 }
+
+pub struct SpanBuilder<const LEN: usize, Wa: WidgetArrLike<LEN, Tag>, Tag> {
+    pub children: Wa,
+    pub dir: Dir,
+    pub gap: f32,
+    _pd: PhantomData<Tag>,
+}
+
+impl<const LEN: usize, Wa: WidgetArrLike<LEN, Tag>, Tag> FnOnce<(&mut Ui,)>
+    for SpanBuilder<LEN, Wa, Tag>
+{
+    type Output = Span;
+
+    extern "rust-call" fn call_once(self, args: (&mut Ui,)) -> Self::Output {
+        Span {
+            children: self.children.ui(args.0).arr.to_vec(),
+            dir: self.dir,
+            gap: self.gap,
+        }
+    }
+}
+
+impl<const LEN: usize, Wa: WidgetArrLike<LEN, Tag>, Tag> SpanBuilder<LEN, Wa, Tag> {
+    pub fn new(children: Wa, dir: Dir) -> Self {
+        Self {
+            children,
+            dir,
+            gap: 0.0,
+            _pd: PhantomData,
+        }
+    }
+
+    pub fn gap(mut self, gap: impl UiNum) -> Self {
+        self.gap = gap.to_f32();
+        self
+    }
+}

src/core/trait_fns.rs

@@ -12,6 +12,7 @@ pub trait CoreWidget<W, Tag> {
     fn offset(self, amt: impl Into<UiVec2>) -> impl WidgetFn<Offset>;
     fn scroll(self) -> impl WidgetIdFn<Offset>;
     fn masked(self) -> impl WidgetFn<Masked>;
+    fn background<T>(self, w: impl WidgetLike<T>) -> impl WidgetFn<Stack>;
 }
 
 impl<W: WidgetLike<Tag>, Tag> CoreWidget<W::Widget, Tag> for W {
@@ -87,20 +88,24 @@ impl<W: WidgetLike<Tag>, Tag> CoreWidget<W::Widget, Tag> for W {
             inner: self.add(ui).any(),
         }
     }
+
+    fn background<T>(self, w: impl WidgetLike<T>) -> impl WidgetFn<Stack> {
+        move |ui| Stack {
+            children: vec![w.add(ui).any(), self.add(ui).any()],
+            size: StackSize::Child(1),
+            offset: 0,
+        }
+    }
 }
 
 pub trait CoreWidgetArr<const LEN: usize, Wa: WidgetArrLike<LEN, Tag>, Tag> {
-    fn span(self, dir: Dir) -> impl WidgetFn<Span>;
+    fn span(self, dir: Dir) -> SpanBuilder<LEN, Wa, Tag>;
     fn stack(self) -> StackBuilder<LEN, Wa, Tag>;
 }
 
 impl<const LEN: usize, Wa: WidgetArrLike<LEN, Tag>, Tag> CoreWidgetArr<LEN, Wa, Tag> for Wa {
-    fn span(self, dir: Dir) -> impl WidgetFn<Span> {
+    fn span(self, dir: Dir) -> SpanBuilder<LEN, Wa, Tag> {
-        move |ui| Span {
+        SpanBuilder::new(self, dir)
-            children: self.ui(ui).arr.to_vec(),
-            dir,
-            gap: 0.0,
-        }
     }
     fn stack(self) -> StackBuilder<LEN, Wa, Tag> {
         StackBuilder::new(self)